The objectives of this project are to clone the vermilion locus of Drosophila, to study the structure and expression of the gene, and to investigate the nature of vermilion mutations that can be suppressed by mutating the suppressor of sable locus. Vermilion encodes the enzyme tryptophan oxygenase which catalyzes the first step in the synthesis of the brown eye pigment. DNA from this locus was cloned from a mutant containing a P element insertion at vermilion by "transposon tagging." The cloned DNA hybridizes to the polytene chromosome band that contains vermilion. Furthermore, DNAs from a number of vermilion mutants show detectable aberrations in the region homologous to the cloned DNA. Several spontaneous mutations at vermilion, sable, purple, and speck are suppressible by mutations at suppressor of sable. Using cloned vermilion DNA probes, we have determined that these suppressible vermilion alleles are DNA insertion mutations, and DNAs from several of these mutants have been cloned. The mutants v1, v2, and vk are insertions of the copia-like element known as 412. The weakly suppressible mutant v36f contains an insertion of the element known as roo or B104. Work is continuing to determine the manner in which these insertions disrupt gene expression.